Results from various investigators are not in accord. Carbohydrate analyses differ by 50 percent and somewhat different N-terminal amino acid sequences are obtained. These differences may reside in a heterogeneity of native transcortins, different members of the family being selected by the various isolation procedures employed. We propose to compare (1) the amino aicd and carbohydrate composition of transcortin isolated by ion-exchange and absorption chromatography and by affinity chromatography, (2) transcortin isolated by different investigators (with their consent), and (3) fetal transcortin (obtained from cord blood). To obtain evidence of the nature of the binding site, we will alkylate transcortin with the 5-oxo-6-diazohexanoate ester of 17-hydroxyprogesterone, cleave the desialated material with cyanogen bromide and isolate and sequence the peptide containing the steroid. In addition, we will investigate the role of carbohydrate in binding cortisol and progesterone by selective digestion with carbohydrases and the role of tyrosine in binding by selective acetylation. We will also attempt to determine the number and location of carbohydrate chains.